The present invention relates to a control system for a power steering system, and more particularly to a control system for providing a compensation command based on a frequency dependent damping (FDD) coefficient and an inertia compensation coefficient.
Electric Power Steering (EPS) systems steering assistance to a driver by providing a specific amount of assist torque to a steering system. The assist torque is provided by an electric motor. However, the motor adds additional motor inertia to the steering system. Specifically, the motor inertia may affect the haptic feel of the steering system. As a result, a driver may need to apply torque to a handwheel in order to accelerate and decelerate the handwheel due to the motor inertia. This condition is sometimes referred to as inertia feel.
Various algorithms have been developed to compensate for the additional motor inertia introduced to the steering system. One approach in particular uses a filter on a motor velocity sensor to emulate a derivative calculation that determines motor acceleration. The motor acceleration is multiplied by the motor inertia, and the product of the motor acceleration and the motor inertia represents the torque required to achieve the acceleration of the motor inertia. This torque is then generated by the motor. Thus, the torque required to accelerate or decelerate the handwheel is provided by the motor, instead of a driver. However, one shortcoming of this approach is that the inertia of the motor is not compensated for until the motor starts moving. The result is a lack of compensation as the motor is initially accelerated or decelerated.
Another shortcoming is that there are often other EPS algorithms that make use of filtered motor velocity. These algorithms, if not properly coordinated with the above-mentioned inertia compensation scheme, may provide unexpected results. One such function may be referred to as frequency dependent damping, which adds a damping compensation torque proportional to high-frequency motor velocity signals.